Rolled condenser



April 1959 F. STEINER ETAL 2,881,373

RQLLED CONDENSER Filed Oct. 30, 1953 Inventor F. STEINER E. MORTEK Attorney United States Patent ROLLED CONDENSER Fritz Steiner and Ernst Mortek, Vienna, Austria, assignors to International Standard Electric Corporation, New York, N .Y., a corporation of Delaware Application October 30, 1953, Serial No. 389,382

Claims priority, application Austria November 17, 1952 3 Claims. (Cl. 317-260) I The invention relates to an electric rolled condenser with a core of special design, this core being used both as a winding core and a balancing or additional capacity.

In various rolled condensers, especially rolled condensers with a dielectric made of synthetic foil, it is convenient to roll the condenser on a winding core.

The winding core may consist either of a metal or synthetic tube or a solid rod. Such cores can be made during the winding process by winding in the first windings a strip of a material having a greater strength than the foil.

The importance of using this type of core particularly in rolled condensers with a polystyrol dielectric is that it prevents an undefined inward shrinking during the heat treatment, thus making it possible to maintain close capacity tolerances if the foil stretching is continued to the point where absolute mechanical strength of the rolled condenser results.

According to the invention, it is proposed to use, instead of the winding cores employed heretofore, winding cores characterized in that they consist of at least one helical-shaped wire, one end of which, the so-called contact end, is connected to one condenser coating and represents an additional capacity with respect to the other condenser coating, which can be varied in a definite manner by subsequent unwinding of the helical-shaped wire core by pulling out the other wire end, the so-called balancing end.

According to another feature of the invention, the winding core may in itself represent a condenser coating, while the roll is wound not with two but with only one metal layer and the total capacity of the condenser may be formed by the oppositely placed single layer. In this case, of course, the connection of the contact end, which remains open, is omitted.

The winding core according to the invention may, according to another feature, be designed in such a manner that the balancing end may be led out through the inside of the helical-wire winding core on the same side as the contact end. If the mandrel is properly designed, the balancing end led inside the winding will cause the latter to be carried along by the winding mandrel, which is a particular advantage of this embodiment example.

According to another embodiment of the invention, the balancing end and the contact end of the winding core according to the invention may be placed on various sides of the winding core.

According to another feature of the invention, in order to obtain a smooth balanced surface and improved mechanical strength, the helical-wire core may be covered with a metallic or non-metallic coating.

The invention will now be described in greater detail with reference to an embodiment example. Variants of the invention will be explained at given points of this description.

The single figure shows a schematic cross section through the complete but not balanced rolled condenser.

ice

According to the invention, winding core 1 is made of helical wire, for example. In the embodiment example, the wire is wound with the turns adjacent to one another. Spaces may also be left between the windings. It is moreover not necessary that the pitch be equal to that of the helical line at every point.

The cross section of the wire may for example be circular, elliptical, square, rectangular or triangular, or it may be tubular.

Any kind of metal may be used for the wire, but metals having good conductivity are to be preferred. According to the invention, it is also possible to use a poor conductor, such as a resistance wire, in order to reproduce special circuits in a simple manner. The use of several metals at the same time, such as a copper wire with a tinned surface, may also be employed.

Winding core 1 according to the invention has two ends, namely contact end 3 and balancing end 2. The function of these two ends will be explained later in the description of the operation of the rolled condenser.

The winding mandrel, not shown, is inserted in winding core 1. The winding mandrel for winding the rolled condenser shown must have a slot along a generatrix for receiving balancing end 2. Balancing end 2 also serves as a drive pin, this being of particular advantage in producing the embodiment.

First of all, it is advisable to wind several layers of dielectric over the winding core. For the sake of clearness, the dielectric is shown in simplified form and is denoted by 5. As usual, the dielectric consists of one or more layers and sections. Thereupon, both metal foils outer foil 6 and efiective foil 7, are placed between dielectric strips 5 and wound up together in a well-known manner. It is advisable to design these metal foils in such a manner that outer foil 6 is sufficiently long and wide so that it overlaps and completely shields efiective foil 7 at the beginning, at the end and at the edges. The connecting tabs for the condenser are not shown. They are applied in the usual manner.

Contact end 3 of winding core 1 is advantageously pressed or hammered flat at its outer end 4, so that it may lie in close contact with the effective foil. It is however possible, according to the invention, to keep the diameter of the outer end of contact end 3 the same as that of the winding wire and to connect this end electrically to effective foil 7 in any other well-known manner.

In the embodiment example shown, balancing end 2 is drawn through the inside of winding core 1 and lies in close contact with the inside of winding core 1.

Because of its position with respect to outer foil 6, winding core 1 has a definite capacity determined by its distance from said foil and its length. This capacity acts additively with the condenser capacity proper, which is formed by the opposite condenser foils if, according to the invention, contact end 3 of winding core 1 is electrically connected to effective foil 7.

After the condenser has been impregnated or heat treated, it is possible, by the design of winding core 1 according to the invention, to shorten winding core 1 by drawing out balancing end 2 and unwinding turns, so that the desired total capacity of the condenser is adjusted by this change in the capacity between the winding core and outer foil 6.

The same effect is obtained if balancing end 2 is led out at the end of winding core 1 lying opposite to contact end 3. However, in this variant of the invention, the advantage of using the balancing end as drive pin during the rolling operation is sacrificed.

Balancing end 2 may be used as a connection instead of a separate connecting tab for eiiective foil 7. For ex- U ample, if two winding cores are used, the balancing ends may be arranged inside the rolled condenser and the contact ends at the ends of the condenser.

In addition, several adjacent winding cores may be arranged inside one another in the form of a multi-pitch helical line. Thus, for example, a double pitch helical line resembles a two-wire winding. In the case of several winding cores, the connections may be made in such a manner that one part is connected to the effective foil and the other part to the outer foil.

According to one variant of the invention, the wind ing-core surface facing the roll or the entire surface of the winding core may be provided with a metal or nonmetal coating or, in the case of spaced windings or windings with a variable pitch of the helical line, the interstices may be filled in with a metallic or non-metallic material. In this way the surface is made smooth and greater mechanical strength is given the winding core. It is of advantage, in order to obtain this embodiment, before rolling the winding core to provide the wire at least partly with a surface whose material, after the rolling operation is complete, is distributed, for example by heat treatment. If non-metallic coatings or fillings are used, it is also possible to use insulated wire instead of bare wire. The insulations of adjacent wires fuse together when the condenser is heat treated and thus form the described coating.

It is obvious that this coating can be applied after the winding core has been rolled up.

When the capacity of the rolled condenser is subsequently varied by unrolling the winding core, the coating or filling between the windings is torn and carried along with the wire.

Winding cores that are not made by actually winding a wire also come within the scope of the invention. Use may also be made of a cylindrical metal sleeve which has helical-shaped slots, the arrangement being such that at the ends the extensions of the parts between the slotted helical lines are carried on the shape of a wire as balancing or contact ends.

Finally, one or more helical lines may be used next to or inside of each other (as in the case of two-wire windings).

From a production standpoint, the condenser according to the invention ofl'ers many savings, since subsequent trimming is possible with few means and, hence, the obtainable rolling tolerances may be wider.

We claim:

1. A variable capacitor comprising a core consisting of wire wound in the form of a closely wound single layer helix, a first metallic sheet constituting one electrode of said capacitor surrounding said core and separated a given radial distance therefrom, a second metallic sheet constituting a part of a second electrode of said pac or s rr n ing sai firs m tallic sheet and separated a given radial distance from it, means connecting one end of said wire to said second metallic sheet to form another part of said second electrode, the other end of said wire extending internally of said helix beyond the end of said wire fastened to said second metallic sheet and adapted to be pulled to unwind said core, whereby the capacity of said capacitor may be selectively varied.

2. The capacitor according to claim 1, and further comprising sheets of dielectric material separating said core from said first metallic sheet and said first metallic sheet from said second metallic sheet.

3, The capacitor according to claim 2, wherein said second metallic sheet is longer and wider then said first metallic sheet and arranged to overlap said first metallic sheet.

References Cited in the file of this patent UNITED STATES PATENTS 35 1,774,875 Evans Sept. 2, 1930 2,614,149 Steyer Oct. 14, 1952 2,644,122 Boardman June 30, 1953 FOREIGN PATENTS 0 629,761 Germany May 11,1936 

